The present invention relates generally to a mobile satellite communication system. More specifically, the present invention relates to a mobile satellite communication system with increased user capacity by allowing frequency re-use through the use of multiple satellites to radiate one signal.
Current mobile satellite communication systems, such as Iridium, Globalstar, and ICO, utilize low-cost user terminals as one of their key system features. To maintain communications linkage with these current mobile systems, the system satellites provide multiple beam and high-gain services to the subscribers. The low-cost and low-gain hand-held terminals utilized by the users of these systems, transmit and receive signals to and from high performance satellites which populate almost the entire hemisphere. Some of these current systems require the usage of at least two satellites to assure a soft hand-over process as the satellites progress from horizon to horizon. As a result, as more satellites come into a user""s field of view (FOV), the satellite system becomes more reliable and available. The satellite constellations provided by these current systems are thus sized to guarantee a minimum number of satellites within a user""s FOV over large coverage areas at all times.
All of these current mobile satellite communication systems, however, suffer from a variety of disadvantages. First, they all have limited frequency resources. Any given frequency over a given ground position can only be utilized by one user at a time. This is true regardless of the sophistication of the system, including systems that utilize multiple beam satellite designs. Even when multiple satellites are available at a given geographic location, the same frequency spectrum cannot be used by more than one nearby user. The availability of multiple satellites merely serves to increase the availability of the system to that user who is assigned the specific frequency spectrum. However, the total capacity of these mobile communication satellite systems is still limited by the inefficient usage of the frequency spectrum. Thus, the potential growth of these current satellite communication systems is inherently limited.
Additionally, current telecommunications systems only allow mobile-to-hub and hub-to-mobile communications in most of the low earth orbit and medium earth orbit mobile satellite constellations. Mobile-to-mobile linkages require multiple hops between hubs. Thus, one user utilizes a satellite at a frequency slot to communicate to his counterpart on the network. Other satellites on or in the same region cannot reuse the same frequency slot for other nearby users. Thus, if a secondary user nearby has a handset that requires a particular frequency, which is being utilized by the first user nearby, the second user is unable to access the system through the same frequency via different satellites. It is therefore desirable to provide a mobile communication satellite system that relaxes these constraints and more efficiently utilizes current mobile satellite communication system resources, while also providing much greater opportunity for system growth.
It is an object of the present invention to provide a mobile satellite communication system with no limitation on frequency re-use for point-to-point communications.
It is another object of the present invention to provide a mobile satellite communication system that utilizes simple and low cost satellite designs.
It is a further object of the present invention to provide a mobile satellite communication system with high system reliability through graceful degradation.
It is still another object of the present invention to provide a mobile satellite communication system wherein the individual satellites and the mobile terminals are of low complexity with the complexity of the system concentrated at the ground hub terminal.
It is yet another object of the present invention to provide a mobile satellite communication system with more accurate capabilities for satellite and user positioning.
In accordance with the objects of the present invention, a novel mobile satellite communications technique for hand-held terminals is provided. The mobile satellite communications system includes a satellite system having a plurality of individual satellites. The plurality of individual satellites are each in communication with a ground telecommunications hub such that a signal processed by the ground telecommunications hub is radiated through multiple paths to a plurality of the individual satellites in the satellite constellation. The radiated signal is then re-radiated by the plurality of individual satellites to a mobile satellite terminal which receives the re-radiated signal from the plurality of individual satellites simultaneously such that the same frequency spectrum may be re-used by another mobile user.
These and other features of the present invention will become apparent from the following description of the invention, when viewed in accordance with the accompanied drawings and appended claims.